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ECE 358: Computer Networks Instructor: Dr. Sagar Naik
Introduction 1-1
https://ece.uwaterloo.ca/~ece358/
About the instructor
Introduction 1-2
Teaching interest:
Research:
ECE 358, ECE 416, ECE 655(Past: ECE 355, ECE 453)
Energy efficiency of smartphones and tablets
Wireless networks: ad hoc, delay-tolerant, sensor, vehicular, peer-to-peer
Smart grids
Performance testing of software, including mobile apps
Teaching Assistants
Introduction 1-3
Atulan Zaman [email protected]
Adel Ghanbari [email protected]
Shilpa [email protected]
Class email: [email protected]
Grading scheme
Introduction 1-4
Mini projects (3): 15% (5 + 5 + 5) group size = 2
Midterm exam: 25%
Final exam: 60% -----------------------------------------------Total: 100%
Classroom protocol
Introduction 1-5
• All cell phones, including mine, must be turned off.
Interference degrades performance.
• No peer-to-peer communication It causes interference.
Introduction 1-6
Connected Society
App
App
App
Online Services
Body Area Network
Smart Grid Internet of Things (IoT)to monitor traffic, environment,water, infrastructure, people….
for smart living
Introduction 1-7
App
App
App
Online Services
LAN: Local Area Network; WLAN: Wireless LAN
LAN
WLAN
Layer-2 (L2) switch
Layer-3 (L3) switch (Router)
Accees Point (AP)
Ethernet/Fibre connectors
Free space
A LAN is a network of computersconnected by means of a wired “broadcast” medium.
A WLAN is a network of computersconnected by means of a wireless “broadcast” medium.
Introduction 1-8
3 Objectives of ECE 358
App
App
App
Online Services
App
1. 1-hop comm to reach the first router
2. Multi-hop comm among routers3. App-App (End-to-End) reliable comm
App
Comp.—Comp. comm
Introduction 1-9
3 Objectives of ECE 358
App
App
App
Online Services
App
1. 1-hop comm to reach first router (Link/MAC)
2. Multi-hop comm among routers (Network)3. App-App (End-to-End) reliable comm (Transport)
App
Comp.—Comp. comm
PhysicalLink/MAC (Ch. 5)
Network (Ch. 4)
Transport (Ch. 3)
App
L2 (Layer 2)L3L4
L1
MAC: Medium Access Control
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
Introduction 1-10
(ISP: Internet Service Provider)
A hierarchical view of the Internet
Introduction 1-11
New
Time
Intro.(5 Hrs)
Link Layer(13 Hrs)
Network(12 Hrs)
Transport(6 Hrs)
App1 App2
45points
101points
53points
45points
StudyPoints
Introduction 1-12
New
Frequently, I will pause to ask: Do you have questions?
More exam-kind questions on homeworks
Note
There are too many acronyms in the field ofcomputer networks.
The course has too much details.
Introduction 1-13
For real engineers …
To other LANs on the Internet
LAN1
LAN2
Introduction 1-14
L2 and L3 switches and connectors
Cisco L3 switch (Catalyst 4948)
48 10/100/1000 BASE-T ports (RJ45)
Mbps (Megabits/sec)
4 1000 BASE-X Small Form-factor Pluggable (SFP) optics ports
Back panel of Catalyst 4948
Dual powersupply
Removablefans
BASE: Baseband Bits are not modulated.T: Twisted pair (copper)
Introduction 1-15
L2 and L3 switches and connectors
24 10/100 BASE-T PoE (Power over Ethernet) ports 2 Gigabit ports 2 Fiber ports
Cisco L2 switch(SF300 24P)
Introduction 1-16
L2 and L3 switches and connectors
Category 6 (Cat.6 on cables) cables support
- 10 BASE-T (Ethernet)- 100 BASE-T (Fast Ethernet)- 1000 BASE-T (Giga Ethernet)- 10 GBASE-T (10 Gigabit Ethernet)
Twisted to cancel out electromagnetic interference.
Common copper connectors …
Cat 5e
Introduction 1-17
L2 and L3 switches and connectors
Common fiber connectors …
GBIC: Gigabit Interface Converter (1 Gbps)
SFP: Small Form factor Pluggable trans. (1 Gbps)
CFP: C Form factor Pluggable (C in Latin = 100) (100 Gbps)
SFP+: (10 Gbps)
Cisco CFP-100G-ER4
Chapter 1Introduction
Computer Networking: A Top Down Approach ,5th edition. Jim Kurose, Keith RossAddison-Wesley, April 2009.
A note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.
Thanks and enjoy! JFK/KWR
All material copyright 1996-2010J.F Kurose and K.W. Ross, All Rights Reserved
Introduction 1-18
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core: network of nets circuit switching, packet switching, network structure
1.4 Delay, loss, and throughput in packet-switched networks Performance metrics
1.5 Protocol layers, service models
Introduction 1-19
What’s the Internet: component view of an ISP
Introduction 1-20
DHCP: Dynamic Host Configuration ProtocolGives your computer an IP address
DNS: Domain Name SystemPerforms mapping:
host name IP addressecemail.uwaterloo.ca 129.97.x.ywww.amazon.com a.b.c.d
Access Network
DHCP
DNS
server
Distribution Network
UW core
Eng.
EIT 4
UW ISP
Regional ISP
Global ISP
coverage,load balancing,reliability
security +connectivity policies
Core Network
Connected to other ISPs
What’s the Internet: component view
protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Ethernet
Internet: “network of nets” loosely hierarchical
Internet standards RFC: Request For Comments IETF: Internet Eng. Task Force
Introduction 1-21
DHCP
DNS
server
Distribution Network
Reg. ISP
Global ISP
Core Network
Connected to other ISPs
Access Network
What’s the Internet: a service view
communication infrastructure enables distributed apps: Web, VoIP, email, games, e-
commerce, file sharing Comm. services provided to apps:
reliable data delivery from source to destination
“best effort” data delivery
Introduction 1-22
What’s a protocol?
Protocols define Format of messages (Message: Header + Optional data) Order of messages sent and received among network entities Actions taken on msg transmission and reception
Introduction 1-23
A protocol is a set of
communication rules.
Protocols run onhosts, switches, routers...
All comm. activities on Internet are governed by protocols.
An Example
TCP connectionresponse
Get http://www.awl.com/kurose-ross
<file>
time
Introduction 1-24
TCP connectionrequest
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction 1-25
The network edge: end systems (hosts):
run application programs e.g. Web, email at “edge of network”
client/server
peer-peer
client/server model client host requests, receives
service from always-on server e.g. Web browser/server; email
client/server peer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype, BitTorrent
Introduction 1-26
Access networks and physical media
Q: How to connect an end system to an edge router?
Introduction 1-27
edge routers
mobile access networks
WiFi
residential access nets DSL (Digital Subscriber Line),
Cable
institutional access networks (school, company)Ethernet
telephonenetwork
homePC
homephone
Internet
DSLAM
centraloffice
DSL: Digital Subscriber Line
Uses existing telephone infrastructure
Introduction 1-28
DSLAM: DSL Access Multiplexer
One home
Point-to-Point Protocol (PPP)
To another home ::
voice
data
DSL modem
splitter
Upstream: up to 1 Mbps (today typically < 256 kbps) Downstream: up to 8 Mbps (today typically < 1 Mbps)
home
cable headend
cable distributionnetwork
server(s)
Introduction 1-29
Cable Network Architecture: Overview
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
Introduction 1-30
home
cable headend
cable distributionnetwork
Channels
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
VIDEO
DATA
DATA
CONTROL
1 2 3 4 5 6 7 8 9
FDM (more shortly):
Introduction 1-31
Cable Network Architecture: Overview
Ethernet Internet access
100 Mbps
100 Mbps
100 Mbps
1 Gbps
typically used in companies, universities, etc
Introduction 1-32
institutionalrouter to institution’s
ISP
server
Early Ethernet
Ethernetswitch
Question: How do nodes efficiently share the medium?
10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet
Wireless access networks
shared wireless access network connects end systems to router via base station aka “access point” (AP)
Introduction 1-33
basestation
router
wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps 802.11ac: 1 Gbps WLAN;
0.5Gbps/host
wider-area wireless access provided by telco operators ~1Mbps over cellular system (EVDO,
HSDPA) LTE (Long Term Evolution)
(On the wired net.)
To Internet
Mobile hosts
EVDO: Evolutionary -- Data Only; HSDPA: High Speed Data Packet Access
Outside ECE 358
Home networksTypical home network components: DSL or cable modem router/NAT (Network Address Translation) In IP layer Ethernet wireless access point
wirelessaccess
point
wirelesslaptops
routerCable modemto/fromcable
headend
Ethernet
Introduction 1-34
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction 1-35
The Network Core
mesh of interconnected routers
Introduction 1-36
the fundamental question: how is data transferred through a net?
circuit switching: dedicated circuit per call: telephone net
packet-switching: data sent thru the net in discrete “chunks”
Network Core: Circuit Switching (not yet there…)
End-end resources are reserved for “call” (aka a session)
Introduction 1-37
call setup required
link bandwidth, switch capacity
dedicated resources: no sharing
circuit-like (guaranteed) performance
Network Core: Circuit Switching
Network resources (e.g., bandwidth) are divided into “pieces”
frequency division multiplexing (FDM) time division multiplexing (TDM)
Introduction 1-38
resource piece remains idle if not used by owning call
pieces allocated to calls
Circuit Switching: FDM and TDM
FDM
frequency
time
TDM
frequency
time
4 users
Example:
Introduction 1-39
Numerical example (Fall 2012 Final Exam)
How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?
Assume that:• all link speeds: 1.536 Mbps (Megabits per second)• each link uses TDM with 24 slots/sec• a user receives one slot every 8 slots in the TDM scheme• it takes 500 msec to establish an end-to-end circuit
Show the details of your calculations.
Introduction 1-40
3/60 marks
7 minutes
Numerical example (Contd.: Answer)
The number of bits transmitted by a user in 1 slot = (1/24)* 1.536 Mbps = 64000 bits.
Introduction 1-41
Therefore, total time needed = 3.33 s + 0.5 s = 3.83 s
A user gets to transmit in 3 ( = 24/8) slots in each second.
So, the amount of data transmitted by a user in 1 second = 3 * 64000 bits.
To transmit 640,000 bits, time needed = Total data / Rate = 640,000/(3*64,000) = 10/3 sec. = 3.33 seconds.
You need 0.5 seconds to establish a connection.
Network Core: Packet Switching
each end-end data stream is divided into packets
resource contention:
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
Introduction 1-42
resources are used as needed
user A, B packets share network resources
each packet uses full link bandwidth
store and forward: packets move one hop at a time node receives complete packet before
forwarding
aggregate resource demand can exceed amount available
congestion: packets queue, wait for link use
Routers ….
Packet Switching: Statistical Multiplexing
sequence of A & B packets has no fixed timing pattern
A
B
C100 MbpsEthernet
1.5 Mbps
D E
statistical multiplexing
queue of packetswaiting for output link
Introduction 1-43
bandwidth is shared on demand: statistical multiplexing.
R1 R2
R3
Packet-switching: store-and-forward
takes L/R seconds to transmit (push out) packet of L bits on to link at R bps
Example: L = 7.5 Mbits (Note: packets are not that long!
~1.5KB is very common) R = 1.5 Mbps transmission delay = 3*5 =
15sec
R R RL
more on delay shortly …
Introduction 1-44
store and forward: entire packet must arrive at router before it can be transmitted on next link
delay = 3L/R (assuming zero propagation delay)
Packet-switching: store-and-forward
Introduction 1-45
Fall 2012 mid-term exam question #1
Introduction 1-46
• Suppose that host A wants to send a 1 Gigabit file to host B.
Link 3R3
Figure 1.
BRouter 2Router 1
Link 1R1
Link 2R2
A
Numerical example: Fall 2012 mid-term exam
•Assume that the propagation delays on the three links are zero seconds. •Make other assumptions as necessary and appropriate.
•The network between A and B has three links (See Fig. 1.) of rates R1 = 4Mbps, R2 = 2Mbps, and R3 = 1Mbps.
“Giga” means 109, “Mega” means 106, and “Kilo” means 103.
•If A sends the file as 1000-byte packets, how long does it take to movethe file from A to B? Show the details of your calculation.
Introduction 1-47
Numerical example: Fall 2012 mid-term examFile size, F = 1 Gigabit = 10^9 bits Packet size, P = 8 x 10^3 bitsPacket count, N = F/P = 125 x 10^3
Approximate solution
Ti = Time to transmit 1 packet over link i.T1 = P/R1 = 8 x 10^3 bits / (4 x 10^6 bps) = 2 x 10^(-3) sec = 2 ms.T2 = P/R2 = 8 x 10^3 bits / (2 x 10^6 bps) = 4 x 10^(-3) sec = 4 ms.T3 = P/R3 = 8 x 10^3 bits / (1 x 10^6 bps) = 8 x 10^(-3) sec = 8 ms.
Host A will take N x T1 = 125 x 10^3 x 2 x 10^(-3) sec = 250 secRouter 1 will take N x T2 = 125 x 10^3 x 4 x 10^(-3) sec = 500 secRouter 2 will take N x T3 = 125 x 10^3 x 8 x 10^(-3) sec = 1000 sec
File transfer time (exact solution: see next page) = 1000.006 s.
Bottleneck link is link 3 so the throughput of the network between A and B is R3.Therefore, file transfer time= F / R3
= (1 x 10^9 bits) / (1 x 10^6 bps)= 1 x 10^3 sec = 1000 sec.
Link 3R3
BRouter 2Router 1
Link 1R1
Link 2R2
A
Introduction 1-48
Numerical example: Fall 2012 mid-term exam
1000.006 s
This is how all the packetsare moved.
Time
Packet switching versus circuit switching
Example: 1 Mb/s link each user:
• 100 Kb/s when “active”• active 10% of time
Packet switching allows more users to use network!
N users
1 Mbps link
Introduction 1-49
…..
circuit-switching: 10 users (= 1Mb/s / 100Kb/s)
packet switching: with 35 users, probability of more than 10 active at same time is less
than .0004.
Packet switching versus circuit switching
great for bursty data: you can support more users resource sharing simpler, no call setup
Introduction 1-50
Q: How to provide circuit-like behavior?bandwidth guarantees needed for audio/video appsstill an unsolved problem (chapter 7)
excessive congestion: packet delay and loss protocols needed for reliable data transfer,
congestion control
Introduction 1-51
Fall 2012 final exam question (6/60 marks)Compare circuit switching with packet switching by identifying five attributes of communication systems. For full credit, state the most important attributes.
Attributes Circuit switching Packet switching
Introduction 1-52
Fall 2012 final exam question (6/60 marks)
Attributes Circuit switching Packet switching
Conn. Estm. Yes No
Resource Res Yes No
Multiplexing Time Division MultiplexingFrequency Division Multiplexing
Statistical Multiplexing
PerformanceGuarantee
Yes No
Number of users
Upper bounded, for a given multiplexing scheme
Not bounded
Resource utilization
Slots can go unused if users do not have traffic
A smaller number of users meansthat they get more share of thebandwidth
Internet structure: network of networks roughly hierarchical
Introduction 1-53
IXP IXP
Large Content Distributor
(e.g., Google)
Large Content Distributor
(e.g., Akamai)
Tier 1 ISP Tier 1 ISP
Tier 1 ISP
Tier-1 ISPs &Content
Distributors, interconnect
(peer) privately
… or at Internet Exchange Points (IXPs)
at center: small # of well-connected large networks “tier-1” commercial ISPs (e.g., Verizon, Sprint, AT&T, Qwest, Level3),
national & international coverage
treat each other as equals (no charges)
large content distributors (Google, Akamai (Netflix: Open Connect), Microsoft)
Canadian Tier-1: MTS Allstream (MTS: Manitoba Telco Service)
Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
….
………POP: point-of-presence
Introduction 1-54
Tier 2ISP
Internet structure: network of networks
Introduction 1-55
Tier 1 ISP Tier 1 ISP
Large Content Distributor
(e.g., Google)
Large Content Distributor
(e.g., Akamai)
IXP IXP
Tier 1 ISP
“tier-2” ISPs: smaller (often regional) ISPs
Tier 2ISP
Tier 2ISP
Tier 2ISP
Tier 2ISP Tier 2
ISPTier 2ISP
Tier 2ISP
Tier 2ISP
tier-2 nets sometimes peer directly with each other (bypassing tier-1) , or at IXP
connect to one or more tier-1 (provider) ISPs each tier-1 has many tier-2 customer nets tier 2 pays tier-1 provider
Tier 2ISP
Internet structure: network of networks
Introduction 1-56
Tier 1 ISP Tier 1 ISP
Large Content Distributor
(e.g., Google)
Large Content Distributor
(e.g., Akamai)
IXP IXP
Tier 1 ISP
Tier 2ISP
Tier 2ISP
Tier 2ISP
Tier 2ISP Tier 2
ISPTier 2ISP
Tier 2ISP
Tier 2ISP
“Tier-3” ISPs, local ISPs customer of tier-1 or tier-2 networks
last hop (“access”) network (closest to end systems)
Tier 2ISP
Internet structure: network of networks
Introduction 1-57
Tier 1 ISP Tier 1 ISP
Large Content Distributor
(e.g., Google)
Large Content Distributor
(e.g., Akamai)
IXP IXP
Tier 1 ISP
Tier 2ISP
Tier 2ISP
Tier 2ISP
Tier 2ISP Tier 2
ISPTier 2
ISPTier 2
ISP
Tier 2ISP
a packet passes through many networks from source host to destination hostIn near future…end-end data
transfer is likely to be like this:
First segment: statistical multiplexing..Middle segment: Light path (i.e. circuit with WDM)Final segment: statistical multiplexing..
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction 1-58
How do loss and delay occur?
packets queue in router buffers (i.e. memory)
A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
Introduction 1-59
1.5 MbpsCorrupted packets are dropped loss
packets queue, wait for turn
packet arrival rate to link exceeds output link capacity
Four sources of packet delay
dproc: nodal processing check bit errors determine output link typically < msec
A
Bnodal
processing queueing
dqueue: queueing delay time waiting at output link for
transmission depends on congestion level
of router
Introduction 1-60
Four sources of packet delay
A
B
propagation
transmission
nodalprocessing queueing
Introduction 1-61
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans = L/R
dprop: propagation delay: d: length of physical link s: propagation speed in medium
(~2x108 m/sec) dprop = d/sdtrans and dprop
very different
R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate
(#packets/s) Traffic intensity: La/R Queuing delay vs. La/R
La/R ~ 0: avg. queueing delay small La/R -> 1: avg. queueing delay large La/R > 1: more “work” arriving
than can be serviced, average
delay infinite! Introduction 1-62
traffic intensity = La/R
aver
age
que
uein
g de
lay
La/R ~ 0
Queueing delay (revisited)
La/R -> 1
“Real” Internet delays What do real Internet delay look like?
3 probes
3 probes
3 probes
Introduction 1-63
C:xyz>tracert u-aizu.ac.jp
For all i: (ith router) sends three packets that will reach router i on path towards
destination router i will return packets to sender sender times interval between transmission and reply.
Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination.
C:xyz>tracert swin.edu.au
“Real” Internet delays and routes
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
* means no response (probe lost, router not replying)
trans-oceaniclink
Introduction 1-64
Packet loss
queue (i.e. buffer) preceding
link has finite capacity
A
B
packet being transmitted
packet arriving tofull buffer is lost
buffer (waiting area)
Introduction 1-65
lost packets may be retransmitted by previous node, by source end system, or not at all
packet arriving to full queue dropped (aka lost)
……
……
……
Throughput
throughput: the rate (bits/time unit) at which bits are transferred between sender/receiver
server sends bits (fluid) into pipe
Introduction 1-66
pipe that can carryfluid at rate
Rs bits/sec)
pipe that can carryfluid at rate
Rc bits/sec)
instantaneous: rate at given point in time (=max rate)
(the output rate of an input/output system)
average: rate over a long period of time
I/OSysteminput
output
Interface capabilities and link quality determine Rs
Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
bottleneck link
Introduction 1-67
the link on end-end path that constrains end-end throughput
Throughput: Internet scenario
10 connections (fairly) share backbone bottleneck link R bits/sec
Rs
Rs
Rs
Rc
Rc
Rc
R
per-connection end-end throughput: min(Rc,Rs,R/10)
Introduction 1-68
in practice:
Rc or Rs is often the
bottleneck
Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge end systems, access networks, links
1.3 Network core circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction 1-69
Why layering?
Very different functionalities are addressed in different layers. Ex.: medium access is very different than routing
Introduction 1-70
Physical
Link/MAC (Ch. 5)
Network (Ch. 4)
Transport (Ch. 3)
App
Modularization facilitates better maintenance and system evolution Ex.: change in network interface does not require TCP
to be modified.
Internet protocol stack (on end devices)
application: supporting network applications FTP, SMTP, HTTP
Introduction 1-71
physical: bits “on the wire”: Ethernet, 802.11 (WiFi)
transport: process-process data transfer TCP, UDP
network: routing of datagrams (packets) from source to destination IP, routing protocols
link: data transfer between neighboring network nodes (MAC/Link)
Physical
Link
Network
Transport
App
ISO/OSI reference model with 7 layers
presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
7. application
6. presentation
5. session
4. transport
3. network
2. link
1. physical
Introduction 1-72
International Standards Organization/ Open System Interconnection
X.400: E-mail envelope
session: synchronization, checkpointing, recovery of data exchange (Ex.: Skype call session)
Internet stack “missing” these layers!
these services, if needed, must be implemented in application
Internetstack
source
applicationtransportnetwork
linkphysical
HtHn M
segment Htpacket(datagram)
destination
applicationtransportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
switch
Encapsulation using headersmessage M
Ht M
Hn
frame
Introduction 1-73
Internet History
1961: Kleinrock - queueing theory shows effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research Projects Agency
1969: first ARPAnet node operational
1972: ARPAnet public demonstration NCP (Network Control Protocol)
first host-host protocol first e-mail program ARPAnet has 15 nodes
1961-1972: Early packet-switching principles
Introduction 1-74
Internet History
1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn - architecture for interconnecting networks
1976: Ethernet at Xerox PARC late70’s: proprietary
architectures: DECnet, SNA late 70’s: switching fixed length
packets (ATM precursor) 1979: ARPAnet has 200 nodes
Cerf and Kahn’s internetworking principles: minimalism, autonomy -
no internal changes required to interconnect networks
best effort service model stateless routers decentralized control
define today’s Internet architecture
1972-1980: Internetworking, new and proprietary nets
Introduction 1-75
Internet History
1983: deployment of TCP/IP
1982: smtp e-mail protocol defined
1983: DNS defined for name-to-IP-address translation
1985: ftp protocol defined
1988: TCP congestion control
new national networks: Csnet, BITnet, NSFnet, Minitel
100,000 hosts connected to confederation of networks
1980-1990: new protocols, a proliferation of networks
Introduction 1-76
Internet History
early 1990’s: ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
early 1990s: Web hypertext [Bush 1945, Nelson
1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of
the Web
late 1990’s – 2000’s: more killer apps: instant
messaging, P2P file sharing network security to forefront est. 50 million host, 100
million+ users backbone links running at
Gbps
1990, 2000’s: commercialization, the Web, new apps
Introduction 1-77
Internet History
2010: ~750 million hosts voice, video over IP P2P applications: BitTorrent
(file sharing) Skype (VoIP), PPLive (video)
more applications: YouTube, gaming, Twitter
wireless, mobility
Introduction 1-78
Next…..
1-hop communication
Introduction 1-79
Multi-hop communication
End-to-end reliable comm. with TCP
Review what you
learned
in 2 weeks.